Khanna A.S. (Ed.) High-Performance Organic Coatings: Selection, application and evaluation

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High-performance organic coatings 397

•

have to travel before descending to the next layer

similar to the expansion of low carbon steel. This does not occur in the

• Low permeation

• Low surface stress

• Extremely high resistance to undercutting

• Abrasion resistance.

Abrasion resistance and low permeation rate are achieved due to the high

being eroded around it. For example, if the abrasion is due to particles of

particle [8].

coating from eroding. This results in good abrasion resistance, much closer

reinforcement within the resin achieves dimensional stability. This property

is important when coatings need machining. Another property is good

resistance to cathodic disbonding, which is due to high electrical resistivity

are:

• Composition – borosilicate glass

• Thickness – 1 to 7 μm

• Particle width variation – trowelling compounds normally use 3.2 mm,

while high build spray applied coatings use 0.4 mm (1/64″). Micronized

glass is used in spray-applied coatings that are typically 45 μm build.

The following coating systems have been established as having all of these

required properties:

can be used as good filler in an organic coating film. However, many of

these have disadvantages in their own right in spite of specific advantages.

same way with granular fillers. The following are the three main properties

• Coefficient of thermal expansion similar to low carbon steel.

These three properties lead to the fourth and fifth properties:

aspect ratio of glass which, unlike granular fillers, protects the resin from

much larger size than the filler used, the resin will be reloaded around the

filler or even the filler particle can be taken away along with the abrasive

Size of flakes, which determines the lateral distance the corrosive ions

• Symmetry of flakes within the binder. The longer path through the

binder can be achieved with a flake of high aspect ratio.

There are several flake materials, which are available in flake form and

Corrosion resistant glass offers the best all-round properties of a flake. If

the glassflake and resins are blended correctly, the compound expansion is

of glassflake- filled coatings:

In the case of a glassflake- filled coating, even if the resin is eroded, glass-

flakes being harder and difficult to erode protect the further layers of the

to that of glass filler than that of binder. The high proportion of flakes

and low permeation. Typical specifications of glassflakes used in coatings

398 High-performance organic coatings

• Styrene based vinyl ester resin

• Styrene based bisphenol-A polyester resin

• Styrene based isophthalic polyester resin

• Special epoxy system.

available for several applications. However, until recently their use was

lated for a wide spectrum of end-usages and are suitable for application

where extreme corrosion resistance and abrasion resistance with excellent

mechanical properties are required.

be incorporated in a range of high-performance binder systems to produce

coatings that offer the following:

• VOC compliance

•

• Superior resistance to water ingress

• Good mechanical properties, especially adhesion, abrasion resistance

• Compatible with cathodically protected steel on immersed structures

• Capable of withstanding a wide range of chemical resistance and high

temperature conditions, depending on the binder system used.

tages include:

• Directional reinforcement

• Increased heat distortion temperatures

• High dimensional stability

• Good weld strength

• Reduced mould shrinkage and warpage

• Excellent thermal, UV and colour stability

• Added isotropic properties

enhance bonding.

more confined to very high-build coatings for specialized applications in

Easy application over a wide range of specified film thickness

or fibre fillers, glassflake imparts unique properties as a reinforcing agent.

• Enhanced fire resistance performance

Based on the above resin systems, various glassflake- filled coatings are

vessel linings and immersion systems. Glassflake coatings can be formu-

Glassflake pigmentation is a primary weapon in formulations, which can

and flexibility

Glassflake is a high aspect ratio reinforcement additive. Unlike granular

Glassflake is manufactured from a modified ‘C’ glass composition in a range

of flake thicknesses and particle size distribution. Its performance advan-

• Increased flexural modules

• Glassflake can be used in conjunction with other fillers and additives.

• Glassflake is compatible with a number of adhesion promoters to

• Glassflake is a natural electrical and thermal insulator.

• Glassflake offers a low coefficient of thermal expansion.

High-performance organic coatings 399

18.6

applications. The various resin systems are epoxies, polyesters and vinyl

esters.

18.6.1 Epoxies

The properties of epoxies enable them to be formulated into coatings to

including:

• Excellent corrosion protection for subsea, splash zone and atmospheric

environments

• Excellent resistance to cathodic disbondment

• Tough and abrasion resistant

• No catalyst storage problems.

However, there are also disadvantages, such as:

• Maximum immersion temperature typically 60°C, and maximum dry

heat resistance typically 120°C

• Chalking and colour retention problems on atmospheric exposure

• Generally poor acid resistance.

18.6.2 Polyesters

Polyesters offer faster curing rates than high solids epoxies, although appli-

of the safety aspects of the catalyst. Isophthalic or bisphenol polyester

resins cured with organic peroxide catalyst offer improvement in perfor-

mance over epoxy in terms of mechanical properties and temperature

resistance.

• Maximum immersion temperature is typically 80°C, and maximum dry

heat resistance is typically 140°C

• Isophthalic polyesters are more resistant to chalking and offer superior

colour retention on atmospheric exposure compared to epoxies.

18.6.3 Vinyl esters

Vinyl esters offer the ultimate performance in terms of chemical and tem-

perature resistance. Maximum immersion temperature is typically 120°C,

and maximum dry heat resistance is typically 150°C.

provide protection over a wide range of specification requirements,

cators need to be sufficiently aware of the relative short pot life and

Different resin systems for glassflake coatings

Glassflake coatings with various resin systems have been in use for various

400 High-performance organic coatings

18.7 Application of various resins

Vinyl ester based products have been established for chemical resistance

with good tensile strength at higher temperatures of 100–120°C for

immersed and 160°C for non-immersed conditions. These products are

suitable for a wide range of chemical environments including strong acids,

strong alkalis, petrochemical service environment and demineralized drink-

ing water. For less aggressive media bisphenol-A resin systems are most

suitable. These are normally used for seawater application, sweet crude oil

service and moderate chemical environments.

Epoxy solvent-free systems give long-term protection against moderate

A very special product, unsaturated ester resinous surface coating, is avail-

coating system is effective in reducing surface roughness and has a hydro-

phobic nature. When compared to metallic surfaces that are highly attrac-

tive to water molecules, the hydrophobic nature of such coatings gives a

low surface attraction and repels water, resulting in lower frictional

losses.

level of improvement in this area without loss of other physical properties

18.8 Formulation issues

known, as is the reinforcement nature of the lamellar pigment. There are,

however, possibilities that the particles of glass can end up misaligned in

they can create a potential fault within the coating, leading to accelerated

defects.

Recent developments have shown increasing promise in the use of poly-

ester/acrylic and vinyl ester/acrylic copolymer binders with 0.4 mm to 3–

parallel to the substrate, thus offering excellent resistance to permeation,

corrosion, abrasion, physical abuse and thermal shock. In each 1 mm thick-

chemical attack with desired physical properties. Some fillers used are stain-

less steel, silicon carbide and metallic filler to give high abrasion resistance.

thereby increasing efficiency and often reducing power requirements. This

coating film to give an extended difficult pathway through the film is well

the film, and if these particles have a length greater than the film thickness,

permeation through the film. This effect can lead to the necessity of apply-

ing very thick films or multi-coat applications to compensate for these

able to reduce fluid friction and micro-turbulence in water transport systems,

The reason for the success of glassflake systems has primarily been their

low permeability. The new series of glassflake linings now offer a very high

such as abrasion and impact resistance, flexibility, ease of application, etc.

The theory of glassflake pigment particles aligning without an applied

4 μm thick glassflakes. Formulators have arranged the glassflakes to lie

ness of lining there are multiple layers of overlapping glassflakes. The

High-performance organic coatings 401

minimum 1 mm lining thickness can be derived from two coats of 500 μm

each. A single coat of 750 μm can also be applied.

18.8.1 Micronized glass

the vinyl ester system. However, in the vinyl ester system zinc phosphate

cannot be incorporated due to its effect on the curing mechanism of the

resin system. These combinations offer:

•

allow

• Film thickness variable from 200 μm to 1000 μm depending on end-use

requirements

• Retention of mechanical properties, abrasion resistance and cathodic

disbondment, coupled with outstanding corrosion resistance.

for zinc phosphate coatings, zinc-rich coatings and several others. Factors

that should be taken into consideration when deciding on levels of glass-

•

which will eventually affect application characteristics.

application in mind. To give an example, an epoxy formulation intended

for anticorrosive protection of structural or immersed steel will be quite

cathodic disbondment performance. However, it is the zinc phosphate con-

tents that are the major contributory factor in cathodic disbondment of

lamellar fillers and zinc phosphate gives a synergistic effect, which offers

It is accepted that the lower aspect ratio of the micronized flake does not

give the same potential diffusion pathway as large flake sizes. Tests have

shown that micronized flake pigmented systems show higher rates of water

absorption and vapour permeability compared with the larger flake.

However, in epoxy systems combination of the micronized flake with other

similar permeability to large flake pigment, reducing the permeability of

Ease of application using smaller spray tips than standard Glassflakes

18.8.2 Glassflake levels

There are no official standards governing glassflake coatings as there are

flakes in a coating are as follows.

Steric effects of glassflake. Overloading will cause physical interference

between flakes, which may in turn give rise to film defects.

There is no principle governing the optimum loading of glassflake. The type

of glassflake and its level of incorporation are to be decided with the end

different in terms of the type and content of glassflake from a vinyl ester

chemical resistant vessel lining. Increasing glassflake levels improves

epoxy glassflakes. Micronized glassflakes do not perform well in polyester

Viscosity increase. Higher levels of glassﬂ ake cause increased viscosity,

402 High-performance organic coatings

remains a critical factor in the performance of these systems.

18.8.3 Primers

and zinc phosphate, a separate primer coat is not necessary from the view-

point of anticorrosive performance. In the case of polyester and vinyl ester

immersion service are not available.

There are several products that are formulated from chemically resistant

ings and lining systems with excellent performance characteristics. Using

coating systems that are applied by brush, airless spray or trowel. The heavy

duty lining versions will outperform conventional linings, often at lower

cost. Special systems formulated from higher chemical resistant resins and

through to the substrate, and these systems therefore provide a viable

alternative to acid-proof brick and tiles.

tion techniques offers:

• outstanding corrosion resistance to a wide range of inorganic and organic

chemicals and fumes

• low permeation to chemicals and fumes

• low shrinkage, leading to stress-free curing

• formation of monolithic coatings

• easy repairability

• resistance to undercutting corrosion.

18.9.1 Chemical resistance

With advancements in coating chemistry, a wide range of coating formula-

tions are available today. These coating systems are based on resin systems

or vinyl ester systems in terms of cathodic disbondment. Dry film thickness

specifications, a vinyl ester based holding primer is suggested to maintain

inert fillers reinforced with woven glass fabric or woven synthetic fibres give

• low coefficient of expansion

In the case of glassflake epoxy materials formulated on a blend of glassflake

the integrity of the blaster substrate prior to the application of the glassflake

coating. Epoxy primers for use under glassflake polyester or vinyl ester in

glassflakes and a wide range of chemically resistant resins to produce coat-

different sizes of glassflakes and varying the addition percentage produce

maximum protection. In addition to glassflakes, carbon flakes and mica

flakes are also used. Aggressive chemicals are prevented from penetration

18.9 Advantages of glassflake coatings

The incorporation of glassflake in the polymer resin with proper formula-

High-performance organic coatings 403

such as polyester, vinyl esters and epoxies [9]. Their resistance to different

chemicals is listed in Fig. 18.5. Figure 18.5 illustrates that epoxies are sus-

ceptible to alkaline environments but are highly resistant to inorganic acids

and solvents. Coating systems formulated using vinyl ester resins and their

of suitability in installation, epoxy resin based coating systems are the most

widely used for the concrete surface.

The versatility of the resin chemistry allows formulators today to formu-

late products to achieve chemical resistance and physical properties to meet

the requirements of aggressive conditions. ASTM G 20 should be used to

determine the chemical resistance of the coatings.

18.9.2 Low permeability and water absorption

Organic coatings should be evaluated for their permeability. The ASTM D

1653 standard should be used to characterize the coating, based on its per-

meability level. The lower the permeability value, the better is the resis-

tance of the coating system.

18.9.3 Bond strength and abrasion resistance

The bond strength of the coating should be evaluated as per ASTM D 4541

standard with adhesion to steel surface. These data should be evaluated for

0.5

1.5

2.5

3.5

Bases

Chemical environment

Chemical resistance index (see key)

Epoxy

Polyester

Vinyl ester

Chlorinated

solvents

Aromatic

solvents

Aliphatic

solvents

Inorganic

acid

Organic

acid

1. Not resistant

3. Conditional resistance

2. Limited resistance

4. Resistance to maximum concentration

18.5 Resistance of resins to chemical environment.

modifications are known for their superior chemical resistance, but because

404 High-performance organic coatings

comparison purposes as the strength of coating may exceed the cohesive

strength of the concrete. ASTM D 4060 should be used to evaluate the

coatings for their abrasion resistance [10]. Typical performance character-

conventional coatings

Studies done by R. Nixon, on the exposure of various coatings to a hydro-

gen sulphide environment in wastewater, relate the permeability of the

coating and the concentration of gaseous H

S in the environment to

the time in service before blistering or failure in the coating was observed.

The study showed that cycloaliphatic amine-cured epoxy with water vapour

permeance of 0.54 perms and average H

S concentration of 35 ppm showed

failures after 14 months of exposure. Coal-tar epoxy with water vapour

permeance of 0.62 perms and average H

S concentration of 37 ppm showed

coating with water vapour permeance of 0.02 perm and H

S concentration

of 50 ppm showed failures after 15 months of exposure [11].

treatment plants

thickness of around 500 to 1000 microns due to constraints caused by their

Characteristics Test method Results

expansion

ASTM D 696 10–15 × 10

−6

/°C

Volume solid ASTM-2697 100% reactive

Temperature resistance 115°C (immersed), 175°C

(non-immersed)

Adhesive strength to steel ASTM C 633 200–250 kg/cm

Shear strength ASTM D 1002 150 kg/cm

Tensile strength ASTM C 638 220 kg/cm

% Elongation at break ASTM C 638 0.4%

Compressive strength ASTM D 695 850–900 kg/cm

Abrasion resistance ASTM D 4060 <200 mg (CS-17 wheel)

Hardness ASTM D 2240 >80 Shore D

Water vapour permeability ASTM D 1653 0.06 gm/m

day mil

Salt spray resistance ASTM B117

Coefficient of linear thermal

0 under film corrosion

Table 18.1 Typical performance characteristics of glassflake coatings

istics of glassflake coatings are given in Table 18.1.

18.10 Performance of glassflake- filled coating against

failures after 12 months of exposure. On the other hand, glassflake- filled

18.11 Application of glassflake coating to wastewater

Traditionally glassflake coatings were required to be specified at dry film

High-performance organic coatings 405

application characteristics. However, this thickness may be required in

some but not all environments. For example, in atmospheric anticorrosive

protection of structural steel, such a thickness can be over-engineered and

that give the required protection without the need to apply more coating

than is necessary. ISO 12944 standards can therefore be made applicable

forming a barrier is of paramount importance in achieving the service life

of the product.

Three types of coating system can be recommended for wastewater treat-

ment plants depending upon the structure/equipment and medium they

handle [12]. These are spray-applied, glasscloth-reinforced and glass mat

coatings.

ness of about 1000–1500 microns, depending upon the service medium

handled.

1000–1500 microns thickness.

where there is strain experienced by a chemical-resistant top coating, a glass

and provide the higher tensile strength required in the crack area. The

coating system is shown in Fig. 18.6.

18.12 Conclusions

meability and high resistance to gaseous environments of high concentra-

tion of H

and H

S in wastewater treatment facilities. With proper

for such specifications. The proper installation of the coating system for

fiers where there is high abrasion, glasscloth reinforcement is recommended.

In structures such as sludge dry beds, junction boxes and crack filling areas,

uneconomic. A range of glassflake coatings are available, at film thicknesses

18.11.1 Spray-applied glassflake coating

Structures in waste treatment plants such as primary effluent collecting

chambers, effluent channels, anaerobic chambers and common effluent

channels should be treated with spray-applied glassflake coating to a thick-

18.11.2 Glasscloth-reinforced glassflake coating

In grit chambers, common effluent boxes, common inlet channels and clari-

The coating system should be with a base coat of glassflake coating, fol-

lowed by glasscloth reinforcement and a top coat of glassflake coating with

18.11.3 Glass mat glassflake coating

mat saturated with resin should be applied over the base glassflake coating.

These glass mat layers isolate the top chemical-resistant glassflake coating

Glassflake coating with proper formulation technique can achieve low per-

406 High-performance organic coatings

installation procedures such as surface preparation and quality control

corrosion in wastewater treatment plants.

18.13 References

1. Nita Bhalla, ‘India’s rivers dying due to sewage’, Hindustan Times, 21 February

2007, p. 10.

2. Jie Liu and C. Vipulanandan, ‘Synergistic protection against microbiologically

University of Houston, Houston, TX.

3. Frederic Duprat, ‘Reliability of RC beams under chloride-ingress’, Construction

and Building Materials, Vol. 21, Issue 8, August 2007, pp. 1605–1616.

308.1, 1998.

5. Oil and Colour Chemists’ Association, Australia, Surface Coatings, Chapman

& Hall, Vol. 28, p. 418.

6. R. Nixon, ‘Coating selection guidelines for changing exposure conditions’,

Corrosion Probe, Journal of Protective Coatings and Linings, May 2001.

epoxy coatings for industrial applications’, Corrosion Science and Engineering,

Indian Institute of Technology, Powai, Mumbai, pp. 10–15.

8. N.L. Thomas, ‘The barrier properties of paints and coatings’, Progress in

Organic Coatings, Vol. 19, 1991, pp. 101–121.

9. Amy Forsgren, Corrosion Control through Organic Coatings, CRC Press, Boca

Raton, FL, 2006, p. 46.

splash zone’, Corrosion Science and Engineering, Indian Institute of Technology,

Powai, Mumbai, India.

11. Steve Davis, ‘Polymer based protection system for wastewater treatment facili-

ties’, PCE, December 1997, p. 27.

Glassflake coating

Glass mat

Glass cloth

Concrete

system.

4. American Concrete Institute, Standard Specification for Curing Concrete, ACI

18.6 Glass cloth and glass mat with glassflake coating installation

measures, glassflake coating can provide a lifetime of over 15 years against

influenced corrosion’, Department of Civil and Environmental Engineering,

7. Lt Sameer Chaudhary, Dissertation on ‘Performance evaluation of glassflake

10. A.S. Khanna, ‘ Glassflake epoxy – an excellent system for offshore platforms